The present invention relates to a method for the spatially resolved examination and evaluation of surface properties, and in particular, surface properties which affect the optical impression conveyed by a surface. The method will be described below with reference to examining motor vehicle bodies. However, reference is made to the fact that other kinds of surfaces may also be examined with the method of this invention.
Methods for examining surface properties are known from the prior art. Herein light is directed at the examined surface and the light reflected or diffused off the surface is detected and evaluated. This evaluation allows in particular a determination of the optical surface properties such as color or gloss. Such determination or characterization is required since motor-vehicle bodies or their paint coatings convey different impressions to the human eye depending on the surface properties or the incident light and the angle of observation, thus requiring an objective characterization.
Lately, paint coatings have been gaining popularity which comprise pigments or so-called flakes. These pigments or flakes include metal particles statistically distributed in the layer of finish or on its surface. More precisely, metal pigments may consist of very thin metal flakes acting as miniature reflectors.
Characterizing and standardizing these types of finishes or measuring the surface properties of these finishes creates problems since, due to distribution, placement, orientation and sizes or proportions of the pigments or flakes, and depending on the incidence angle of the light, minor variations of the viewing angle may already result in an observer getting different impressions of colors and lightness.
Manufacturers use, among other things, finishes containing interference pigments which, when viewed on large surface areas, result in color gradients at more or less precisely specified color change angles (flop). This may lead to largely different color impressions which in turn leads to varying overall impressions of the lightness or color of the finished surfaces.
These effects and different perceptions of surfaces caused for example by different densities, distribution, compositions and structures of finish additives such as flakes or effect pigments cannot be detected with prior art methods since the respective detection means only supply information on the composite intensity of the light incident from various locations on the measuring surface i.e. they integrate intensity without spatial resolution.
Furthermore, surface properties vary with the location and the observation angle, and prior art methods do not provide feedback to common parameters, in particular not to the parameters of general color theory.
It is therefore the object of the present invention to include in the examination of surface properties, a resolution and evaluation of the different optical impressions caused specifically by location-specific surface properties such as the distribution, placement, and orientation of effect pigments or flakes and observing the surfaces for example, at different solid angles or illumination.